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J Thorac Cardiovasc Surg 1997;113:215-216
© 1997 Mosby, Inc.
BRIEF COMMUNICATIONS |
London, United Kingdom
Received for publication Jan. 10, 1996 Accepted for publication June 20, 1996 Address for reprints: U. H. Trivedi, FRCS, Department of Cardiothoracic Surgery, St. Thomas' Hospital, Lambeth Palace Road, London, SE1-7EH, England.
Manipulation of the heart and ascending aorta during cardiac operations is an important cause of cerebral emboli.
1,2 To date there has been no reported study on the influence of aortic cannulation technique and the prevalence of cerebral microemboli. We compared the production of emboli, measured in the left middle cerebral artery with transcranial Doppler imaging between the side-clamp technique of aortic cannulation and the stab technique. Both techniques involve trauma to the aortic wall and the possibility of releasing atheromatous debris and of allowing air to enter during the introduction of the cannula. Transcranial Doppler ultrasonography is unable to differentiate gaseous from particulate emboli accurately, but it is a useful method to measure the total number of emboli that reach the brain. Because the middle cerebral artery supplies 80% of the ipsilateral cerebral hemisphere, measurement of emboli within this vessel will reflect the total embolic load for each hemisphere.
Patients and Methods
Twenty patients undergoing elective cardiac operations were prospectively randomized to either the stab (group S) or side-clamp (group C) technique of aortic cannulation. Cannulation was done by one of two senior surgeons (J. R. and G. C.) in equal numbers with each technique, and both surgeons were equally conversant with both techniques. All patients were undergoing first-time elective operation, and those with cerebrovascular disease were excluded.
The two cannulation techniques are similar, but in the stab technique a transverse incision is made in the aorta with a scalpel and as the scalpel is withdrawn the aortic cannula is introduced through the incision. In the side-clamp technique, a Cooley side-biting clamp is used to exclude a portion of the aortic wall, which is then incised vertically, and as the side clamp is released the aortic cannula is inserted. A Sarns 24F gauge cannula (3M Health Care, Ann Arbor, Mich.) was used for all cases. The left middle cerebral artery was chosen because it provides the appropriate embolus-to-blood ratio to maximize embolus detection and has been used in a number of previous studies that examined emboli during cardiopulmonary bypass. 3 Emboli were identified by their short duration, characteristic "chirp," and amplitudes greater than or equal to 10 dB from the background Doppler signal. 4 The audio signal was recorded for 2 minutes before cannulation and for 2 minutes after cannulation. Emboli were subsequently counted by an independent, experienced observer blinded to the cannulation technique (U. T.).
Results are expressed as median with interquartile (IQR) and absolute (AR) ranges. Emboli counts were compared with a Mann-Whitney U test. Comparison of proportions was made by 
2 test. A probability of less than 5% (p < 0.05) was considered significant.
Results
There were no major differences in patient characteristics (Table I) All patients, except one, were undergoing elective coronary artery bypass operation. All cannulations were uncomplicated. There were significantly fewer emboli with the stab technique (median 1, IQR 0 to 2, AR 0 to 4) compared with the number with the side-clamp technique (median 11, IQR 2 to 25, AR 0 to 39) (p = 0.01) (Fig. 1) The one patient who underwent aortic valve replacement was in group C and had one embolic event associated with cannulation.
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Microemboli occur at various stages of cardiac operations, principally at cannulation, commencement of cardiopulmonary bypass, and, maximally, on filling and subsequent beating of the heart. In coronary artery bypass operations cannulation is the third most embolic procedure after removal of partial aortic occlusion clamps and cardiac manipulation, and patients with embolic counts greater than 60 have a significantly higher risk of morbidity and mortality. 2
The validity of Doppler ultrasonography in emboli detection during cardiopulmonary bypass is established. 1 In our study we limited the period of observation to that covering aortic cannulation. All aortas were deemed to be normal by palpation, which, although not as accurate as intraoperative ultrasonography, would be sufficient to detect any gross pathologic condition.
If one takes the threshold embolic load to be 60 emboli, 2 then in group C aortic cannulation accounted for 18.3% of the level versus 3.3% in group S. With both cannulation techniques it is possible to have both gaseous and particulate emboli. We believe that both types of emboli are involved during cannulation. In group C we did observe embolic signals with the application of the aortic side clamp. It may be that with the side-clamp technique a greater proportion of the emboli are of a particulate nature than with the stab technique. We conclude that the stab technique is associated with significantly fewer cerebral microemboli, with a possible reduction in morbidity. It should be used in preference to the side-clamp technique.
Acknowledgments
We thank Drs. O'Riordan, Shabbo, Venn, and Young for permission to include their patients in this study.
References
This article has been cited by other articles:
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  M. A. Borger, R. L. Taylor, R. D. Weisel, G. Kulkarni, M. Benaroia, V. Rao, G. Cohen, L. Fedorko, and C. M. Feindel DECREASED CEREBRAL EMBOLI DURING DISTAL AORTIC ARCH CANNULATION: A RANDOMIZED CLINICAL TRIAL J. Thorac. Cardiovasc. Surg., October 1, 1999; 118(4): 740 - 745. [Abstract] [Full Text] [PDF]
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 M. Ura, R. Sakata, Y. Nakayama, T.-A. Miyamoto, and T. Goto Extracorporeal circulation before and after ultrasonographic evaluation of the ascending aorta Ann. Thorac. Surg., February 1, 1999; 67(2): 478 - 483. [Abstract] [Full Text] [PDF]
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